Bacterial Micro Machines Turn Tiny Gears

The power of swimming bacteria can be harnessed to turn tiny gears, opening the possibility of building hybrid biological machines at the microscopic scale.

The gears, just 380 micrometers in diameter, are turned by the collective swimming motion of bacteria a million times lighter than the gears themselves, scientists announced in a paper Monday in the Proceedings of the National Academy of Sciences.

The rotational velocity of the objects can be controlled by altering the levels of air and nitrogen in the liquid solution. In a sense, the Argonne National Laboratory scientists have almost created living micro machines.

“Our discovery demonstrates how microscopic swimming agents, such as bacteria or man-made nanorobots, in combination with hard materials can constitute a ‘smart material,’ which can dynamically alter its microstructures, repair damage, or power microdevices,” said Argonne National Laboratory physicist Igor Aronson in a press release.

An individual bacterium’s motion appears random. However, at a concentration of about 10 billion bacterial cells per cubic centimeter, the organisms begin to swim together in what the researchers described as “self-organized, large-scale vortices.” It’s that collective motion that powers the gears’ movement. In their experiments, the motion petered out if the concentration was increased to anything beyond 40 billion bacteria per cubic centimeter, as the organisms appear to shift their behavior toward creating biofilms.

While scientific understanding of collective bacterial behavior is still limited, the new paper provides a powerful demonstration that it may be possible to control them with some precision.

“The ability to harness and control the power of bacterial motions is an important requirement for further development of hybrid biomechanical systems driven by microorganisms,” Aronson said.

By experimenting with the type of gear, the amount of bacteria and the oxygen levels in the solution, they were even able to power multiple gears. Even so, the total power the gear extracts from the motion of the bacteria is only on the order of a quadrillionth of a watt.

That’s too small to power any real-world machine, but the scientists hope that such tiny motors could be useful for microfluidic devices or fluid mixers. At a more fundamental level, they also highlight the power of collective movements in bacteria.